Magnetic focussing field arrangements for cathode ray tubes



Dec. 17, 1957 D. H. COVILL 2,817,034

MAGNETIC FOCU SSING FIELD ARRANGEMENTS FOR CATHODE RAY TUBES Filed 001;.8, 1953 Inventor Attorney United States Patent MAGNETIC FOCUSSING FIELDARRANGEMENTS FOR CATHODE RAY TUBES Dennis Henry Covill, Barnet, England,assignor to A. C. Cossor Limited, London, England, a British companyApplication October 8, 1953, Serial No. 384,894

Claims priority, application Great Britain October 23, 1952 9 Claims.(Cl. 313-84) The present invention relates to improvements in magneticfocussing field arrangements for cathode ray tubes.

In operation of a cathode ray tube the beam requires to be focussed in aspot on the tube screen and it is known to employ an annulus or annuliof a permanent magnetic material consisting of oxidic ceramics notcontaining any nickel or cobalt, one example of this kind of materialbeing that referred to under the registered trademark Ferroxdure, forproviding the magnetic focussing field in a television cathode ray tube.

In addition to means for focussing the beam spot on the tube screen atelevision cathode ray tube generally requires an arrangement forcentering the beam spot on the tube screen in the absence of applieddeflecting voltages.

There has previously been used in conjunction with Ferroxdure annulimounted on the neck of a cathode ray tube a centering arrangement forthe beam spot formed on the tube screen which arrangement comprised twothin apertured discs positioned on the tube neck to the side of theannuli nearer the screen, the discs being permanently magnetised suchthat when mounted on the tube neck the direction of magnetisation wasperpendicular to the axis of the tube neck, the discs being angularlyrotatable on the tube neck for centering the beam spot.

It is an object of the present invention to economise in the length ofcathode ray tube neck taken up by a centering arrangement used inconjunction with an annulus or annuli of a material such as that knownas Ferroxdure.

According to the present invention there is provided for use incentering the beam spot formed on the screen of a cathode ray tube anarrangement which comprises a first annulus of a material such as thatknown as Ferroxdure, a second annulus of magnetic material mounted in aconcentric manner with respect to said first annulus so as to lie withinthe tube neck length taken up by the said first annulus or the tube necklength taken up by a plurality of said first annuli, and a locatingdevice whereby there can be produced relative angular rotation betweenthe first annulus and the second annulus about a common axis and alsotilting of the second annulus with respect to the first annulus.

Preferably the first annulus is stationary with respect to the cathoderay tube neck while the second annulus is movable with respect to theneck.

It is preferably arranged that the axis about which the second annulustilts is, for all positions of rotation of said second annulus, adiameter of said first annulus. The locating device may be madedependent on a frame member which is used for supporting the firstannulus with respect to the tube neck. The locating device may comprisea further annular member concentric with and rotatable with respect tothe first annulus, said further annular member having two extending lugslocated substantially diametrically with respect to the first annulusfrom which lugs said second annulus is supported.

Tilt of the second annulus with respect to the first annulus may beobtained through an adjustable screw the ice end of which bears on oneof the said annuli and a bias spring device may be provided to urge oneof said annuli up against the screw end. The adjustable screw may bemounted on the said further annular member to be rotatable therewith.The mounting member for the adjustable screw may provide means by whichthe second annulus can be rotated with respect to the first annulus.

The said first annulus may be axially displaceable for focussing thebeam spot on the tube screen on a further annulus of a material such asFerroxdure, or further such annuli, may be provided and arranged to beaxially displaceable for effecting focussing of the beam spot on thetube screen.

Reference is now made to the accompanying drawings which illustrate anembodiment of the present invention here given byway of example,

Fig. 1 being a side elevation and Fig. 2 is an end view as seen from theleft of Fig. 1.

A cylindrical member of non-magnetic material indicated at 10 is of aninternal diameter such that it is a loose fit on the neck of atelevision cathode ray tube. It has an octagonal end plate 11 ofnon-magnetic material riveted to it, this end plate 11 serving as aframe member for positioning the arrangement on to the cathode ray tubeneck. There is secured to the end plate 11 by a hardening glue materiala first annulus of Ferroxdure indicated at 12, the inside dimension ofthis first annulus making it a. close fit to the outer surface of thecylindrical member 10.

A second annulus of magnetic material indicated at 13 is mounted in aconcentric manner with respect to the first annulus 12, this secondannulus 13 taking up but a part of the axial distance occupied by thefirst annulus 12. This second annulus 13 has two pairs of diametricallyopposed circular apertures indicated at 14 through which projectgripping fingers of lugs indicated at 15 extending laterally from afurther annular member 16. This further annular member 16, which is ofnon-magnetic material, is supported from the end plate 11 by a number ofspring retaining members indicated at 17 into the open end portions 18of which the further annular member 16 fits; by this means the furtherannular member 16, while held close to the end plate 11, can be rotatedaround the first annulus 12. Angular rotation of the further annularmember 16 with respect to the first annulus 12 causes correspondingrotation of the lugs 15 which rotate with them the second annulus 13.

Fixed to one part of the circumference of the further annular member 16is a laterally extending shifting member indicated at 19; angularrotation of further annular member 16 can be obtained by finger pressuresuitably applied to shifting member 19. An adjustable screw indicated at20 is threaded through a tapped insert 21 fitted to a radially extendingportion of shifting member 19 and is arranged to have a substantialcomponent of move ment parallel with the axis of the sleeve 10. The endof adjustable screw 20 bears on the second annulus 13 and a bias springindicated at 22 is held between a collar on adjustable screw 20 and anaperture in the second annulus 13 through which the bent-over end ofbias spring 22 is hooked.

Rotation of the adjustable screw 20 in its tapped insert 21 varies thepressure exerted on the second annulus and causes a tilt of the secondannulus about the axis provided by the extending lugs 15; as these lugsare substantially diametrically opposed the tilt of the second annulus13 resulting from such rotation of the adjustable screw 20 is alwayssubstantially symmetrically about a diameter of the first annulus 12 inall positions of angular rotation of the second annulus 13 with respectto the first annulus 12.

It will be seen that further annular member 16 locates the secondannulus 13 with respect to the first annulus 12,

Also it will be seen there is provided a locating device havingadjustable means whereby by manual adjustment, as by suitable fingerpressure applied to 19 "and adjustment of screw 20, there is obtainedangular rotation and tilting of the second annulus 13 with respect tothe first annulus 12.

There is also provided on the cylindrical member another Ferroxdureannulus indicated at 23, like magnetic poles of annuli 12 and 23 beingadjacent one another. This Ferroxdure annulus 23 is held by hardeningglue to a non-magnetic end plate 24 which extends radially from a sleevemember 25 which is a rotatable fit on cylindrical member 10. The sleevemember 25 has three locating screws indicated at 26 each riding in oneof three portions of a locating spiral groove indicated at 27 providedin cylindrical member 10. A radially extending arm 28 screwed on to endplate 24 enables the Ferroxdure annulus 23 to be radially rotated andthus axially displaced in its spiral groove 27 along cylindrical member10. The portion of the extending arm 28 by which it is turned by hand isprovided with an insulating cover indicated at 29.

When extending arm 28 is rotated axial displacement of the Ferroxdure"annulus 23 occurs with respect to the first Ferroxdure annulus 12 andsuch axial displacement can be utilised for focussing the beam spot onthe screen of the television cathode ray tube.

I claim:

1. An arrangement for use in centering the beam spot formed on thescreen of a cathode ray tube which arrangement comprises the combinationof a first annulus of a permanent magnetic material, a second annulus ofmagnetic material mounted in a concentric manner with respect to saidfirst annulus and located within the tube neck length taken up by thesaid first annulus, means mounting said annuli for relative angularrotation between the two annuli about the axis of the tube neck, andmeans pivotally mounting the second annulus for tilting about a diameterof the second annulus with respect to the first annulus.

2. An arrangement for use in centering the beam spot formed on thescreen of a cathode ray tube which arrangement comprises the combinationof a plurality of first annuli of a permanent magnetic material, asecond annulus of magnetic material mounted in a concentric manner withrespect to one of said first annuli and located within the tube necklength taken .up by said plurality of first annuli, a locating devicefor said second annulus by which there can be produced relative angularrotation between the said one annulus and the second annulus about theaxis of the tube neck, and means pivotally mounting said second annulusfor tilting about a diameter of said one annulus.

3. An arrangement according to claim 1 wherein the first annulus ismounted stationary with respect to the cathode ray tube neck, and thesecond annulus is mounted for movement with respect to the cathode raytube neck.

4. An arrangement according to claim 2 wherein the plurality of firstannuli are mounted stationary with respect to the cathode ray tube neck,and the second annulus is mounted for movement with respect to thecathode ray tube neck.

5. An arrangement for use in centering the beam spot formed on thescreen of a cathode ray tube which arrangement comprises the combinationof a first annulus of a permanent magnetic material, a second annulus ofmagnetic material mounted in a concentric manner with respect to saidfirst annulus so as to lie within the tube neck length taken up by thesaid first annulus, an annular frame surrounding the neck portion ofsaid tube and supporting said first annulus in concentric relation Withsaid neck portion, first means carried by said annular frame andmounting said second annulus upon said frame for rotation with respectto said frame and about the axis of said neck portion, and second meanscarried by said frame and pivotally mounting said second annulus fortilting about a diameter of said first annulus.

6. An arrangement according to claim 5 wherein said first meanscomprises a further annular member mounted concentric with and rotatablewith respect to the first annulus, and said second means comprises twoextending lugs carried by said further annular member and locatedsubstantially diametrically with respect to the first annu: lus, andpivotally supporting said second annulus for tilting with respect tosaid first annulus.

7. An arrangement according to claim 1 and including means for tiltingthe second annulus with respect to the first annulus comprising anadjustable screw mounted with the end thereof bearing on one of the saidannuli, and a bias spring device urging said annulus up against thescrew end.

8. An arrangement according to claim 1 wherein a further annulus of apermenent magnetic material is provided and arranged to be axiallydisplaceable for effecting focussing of the beam spot on the tubescreen.

9. An arrangement according to claim 2 wherein a further annulus af apermanent magnetic material is provided and arranged to be axiallydisplaceable for effecting focussing of the beam spot on the tubescreen.

References Cited in the file of this patent UNITED STATES PATENTS2,418,487 Spoul Apr. 8, 1947 2,533,688 Quam Dec. 12, 1950 2,568,668Steers Sept. 18, 1951 2,580,606 Schiel et a1. Jan. 1, 1952 2,581,657Heppner Jan. 8, 1952 2,591,820 Jackson Apr. 8, 1952 2,717,324 Hall Sept.6, 1955 FOREIGN PATENTS 530,914 Great Britain Dec. 24, 1940'

